1. Field of the Invention
This invention relates to a combination mass transfer and pump apparatus, which in a single step actively mixes a first mass and a second mass and simultaneously pumps one of the first mass and the second mass through the apparatus. More particularly, this invention concerns a combination mass transfer and pump apparatus substantially comprising a housing and at least one distributor element having a plurality of selectively fluid-permeable membrane elements carrying the first mass, wherein the at least one distributor element is agitated within the second mass such that the first mass and/or the second mass diff-use across the plurality of the selectively fluid-permeable membrane elements and in the same step the second mass is pumped through the housing.
2. Description of the Related Art
Mass transfer apparatus can take the form of a membrane oxygenator, which is used to oxygenate blood. Oxygenation of blood is important, for example, in performing surgical procedures, such as open heart surgery, where the heart is stopped and the patient""s blood is pumped artificially, requiring oxygenation. One type of conventional membrane oxygenator employs bundles of stationary hollow fibers retained within a cylindrical housing wherein oxygen is pumped through the hollow fibers in the same direction as the blood being pumped through the oxygenator housing. The hollow fibers consist of microporous membranes, which are impermeable to blood and permeable to gas. Gas exchange takes place when venous blood flows through the housing and contacts the hollow fibers. Based on the law of diffusion, oxygen diffuses across the hollow fiber walls and enriches venous blood in contact with these hollow fibers. Examples of this type of membrane oxygenator are described in U.S. Pat. No. 4,620,965 issued to Fukusawa et al. and U.S. Pat. No. 4,698,207 issued to Bringham et al. The disadvantage of this type of membrane oxygenator is that a relatively thick blood boundary layer is formed around the hollow fibers, which retards oxygenation of blood that does not directly contact the hollow fibers.
In order to disrupt the blood boundary layer, another type of conventional membrane oxygenator oxygenates blood by directing blood flow substantially perpendicular or at an angle to the hollow membranes carrying the oxygen. Examples of this type of membrane oxygenator are described in U.S. Pat. No. 4,639,353 issued to Takemura et al., U.S. Pat. No. 3,998,593 issued to Yoshida et al. and U.S. Pat. No. 4,490,331 issued to Steg, Jr. Drawbacks to these designs include the need for a large priming volume and large blood-biomaterial exposure area, and the tendency for the permeability of the hollow membranes to decrease over time, causing the oxygenator to become less efficient.
Yet another type of membrane oxygenator discloses moving a part of the oxygenator in order to provide increased mixing of blood and oxygen. Examples of this type of membrane oxygenator are described in U.S. Pat. Nos. 3,674,440 and 3,841,837 issued to Kitrilakis and Kitrilakis et al., collectively, (the xe2x80x9cKitrilakis Patentsxe2x80x9d) and U.S. Pat. No. 3,026,871 issued to Thomas (the xe2x80x9cThomas Patentxe2x80x9d). The Kitrilakis Patents disclose a blood flow path positioned around a rotor, wherein the blood flow path and the oxygen flow path is separated by a non-porous membrane layer through which the blood cannot flow. The blood flow travels substantially parallel to the oxygen flow and rotation of the rotor causing mixing by a shearing effect. A characteristic of this device is the use of structures with a wafer-like membrane to separate the blood from the gas phase. In contrast, a distinguishing characteristic of the current device described herein is the use of hollow fiber membranes that both improve pumping action and significantly increase the amount of surface area available for mass transfer. Although the Kitrilakis oxygenator may provide a degree of mixing of the blood, this type of mixing may lead to destruction of red blood cells. While hollow fiber membranes have been and are currently used to oxygenate blood, the devices in which they are used require a separate blood pump, and existing adult units require approximately 2-3 m2 of surface area from the fibers. In contrast, the present invention requires no separate pump, and as little as 0.5 m2 of surface area from the hollow fiber membranes.
The Thomas Patent discloses rotating a single, cylindrical, semi-permeable membrane containing oxygen in a housing wherein blood contacts and flows over the membrane and oxygenation of the blood occurs across the rotating membrane. Disadvantages of this type of membrane oxygenator are that it too tends to form a blood boundary layer along the surface of the membrane. The diffusion of oxygen and carbon dioxide through this blood boundary layer is poor due to the thickness of the boundary layer. Furthermore, since blood films form along the surface of the membrane cylinder there is no mechanism for creating across flow component to disrupt the static boundary layer. Accordingly, the overall oxygen and carbon dioxide transfer of this device is poor and the device requires large priming volumes in order to be properly operated.
Yet another type of blood oxygenator device comprises short microporous fiber layers which are folded, twisted and woven around a hollow shaft that carries the inlet and outlet gas flows. The device is implanted into the vascular system of a patient and rotated to cause mixing of the blood. This type of device is explained in greater detail in xe2x80x9cA Dynamic Intravascular Lung,xe2x80x9d ASAIO Journal, 1994. A disadvantage of this type of blood oxygenator is that only limited number of fiber layers can be incorporated into the device. This restriction occurs because anatomical space is limited and results in insufficient oxygenation/decarbonation of blood. Furthermore, the rotation of the device within the blood vessel may destroy the cells lining the blood vessel.
With the exception of the Kitrilakis device, all of the blood oxygenators mentioned above require a separate pump apparatus to propel the blood through the oxygenator. Some blood oxygenators even employ two separate pump apparatus, wherein a venous pump is used to pump venous blood to the oxygenator and an arterial pump is used to pump the oxygenated blood from the oxygenator to the patient""s arteries. Examples of this type of pump-oxygenator system are disclosed in U.S. Pat. Nos. 3,907,504 and 3,927,980 issued to Hammond et al. and Leonard, respectively. The major disadvantage of pump-oxygenators that employ a multiple step process to pump and oxygenate the blood is that blood may be damaged. Also, this type of approach requires considerable fluid volume to prime the pumps, which leads to clinical complications, difficulty in patient management, and a bulky construction.
Nowhere in the cited related art is there disclosed a combined mass transfer and pump apparatus which effectively oxygenates and pumps blood in one step to sustain a patient for an extended duration, wherein the apparatus is a compact unit. Therefore, there is a definite need for this combination pump-oxygenator, which provides for effective oxygenation/decarbonation and pumping of blood as disclosed in the present invention.
Accordingly, the present invention provides an apparatus that simultaneously transfers mass between two fluids and simultaneously pumps one of the two fluids through a housing in a single-step. The apparatus of the present invention substantially comprises a housing defining a fluid path, at least one distributor element having a plurality of selectively fluid-permeable membrane elements carrying a first fluid such that when the at least one distributor element is agitated within the housing, active mixing of the first and the second fluids occurs, as well as simultaneous pumping of the second fluid through the housing.
Preferably, the distributor element has an inner ring and an outer ring that are concentrically spaced with respect to one another such that they define a fluid supply plenum and a fluid return plenum. The distributor element further includes a fluid return spoke and a fluid supply spoke that are in fluid communication with the fluid return plenum and the fluid supply plenum, respectively.
The present invention optionally provides for a plurality of distributor elements thus, providing additional selectively fluid-permeable membrane elements and increased surface area at which oxygenation/decarbonation of the blood takes place. The specific number of distributor elements is dependent upon the amount of surface area necessary for the specific patient. For example, a larger patient requires greater oxygen delivery and thus, more surface area where the oxygenation/decarbonation takes place, however, less surface area is necessary for a smaller patient. Further, the present invention provides for the surface area of the selectively fluid-permeable membrane elements to be increased by increasing the number of selectively fluid-permeable membrane elements on each distributor element. Also, selectively fluid-permeable membrane elements can cover both the first face and/or second face of each of the distributor disk. A plurality of layers of the selectively fluid-permeable membrane can cover the first face and /or second face of the distributor elements.
The present invention provides for the selectively fluid-permeable membrane elements to be substantially perpendicular to the bulk fluid flow of the first fluid such that there will be cross flow.
The present invention provides for the selectively fluid-permeable membrane elements to be permeable to gas and impermeable to liquids, such as whole blood when the present invention is used in a blood oxygenator. The blood pump-oxygenator of the present invention provides for the plurality of selectively fluid-permeable membrane elements to be microporous such that the fibers are selectively permeable to the desired fluids. The present invention further provides for the opportunity of the surfaces of the selectively fluid-permeable membrane elements to be coated with a material, which would decrease the tendency for performance degradation over time. An example of the type of material used for these purposes is silicone rubber, although numerous other polymer coatings could be used. However, if the present invention is utilized solely for its pumping capabilities, the rotating disk is preferably porous, but made of material that but for the porous design, is otherwise impermeable to fluids.
In addition to continuous rotation, the present invention further provides for the plurality of rotors being rotated in a back and forth motion such that the rotors repeatedly rotate approximately 360 degrees or less, and then reverse direction, resulting in the blood being agitated via the relative motion of the disk to the blood and the blood boundary layer being disrupted. If the forward and back rotation angles differ, pumping may be affected through an absolute precession of the rotor.
The present invention provides an alternative embodiment, which can be used, solely for pumping blood. This alternative embodiment would substantially comprise a housing defining a fluid path, a rotor, at least one rotor hub on which is mounted the rotor and defining a fluid path and preferably having the selectively fluid-permeable membranes taking the form of a plurality of porous fibers attached to the rotor.
An alternative embodiment would utilize additional layers of fluid-impermeable membrane elements to provide a heat exchanger function. Such layers of additional fluid impermeable membrane elements could be interspersed within the mass exchange layers or constitute a separate thermal regulation member. Alternatively, mass exchange fibers can be positioned on only one side of the distributor element and heat exchange fibers on the other forming another type of integrated heat exchanger.
The present invention further provides an embodiment that can be used for mass transfer. For example, if baffles are positioned adjacent to the distributor elements the intrinsic pumping capability of the present invention will be decreased and an additional pumping element may be required.
The present invention further provides for a method of simultaneous mass transfer and pumping.
The present invention provides a blood pump-oxygenator that can be used to treat patients having acute as well as chronic lung diseases.
The present invention further provides a method of cardiopulmonary bypass support that can be used to support the cardiac surgical patient.
The present invention further may optionally be employed with the use of a xe2x80x9csmart controlxe2x80x9d system to provide an automated control of the principal portions of the cardiopulmonary bypass circuit.
The present invention further provides a method of renal dialysis to treat the blood of patients who suffer from some form of kidney dysfunction.
The present invention further provides a method of liver assist that can be used to treat the blood of patients suffering from hepatic deficiencies.
Other details, objects and advantages of the present invention will become more apparent with the following description of the present invention.